This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-153744, Jun. 1, 1999, the entire contents of which are incorporated herein by reference.
This invention relates to a distance-measuring apparatus used in an image pickup device, such as a silver bromide camera, a digital camera, or a video camera, and more particularly to a distance-measuring apparatus realizing so-called multi-autofocus (hereinafter, referred to as multi-AF) for measuring subject distances at points on the shooting screen. More specifically, this invention relates to a measuring-distance characterized by having a wide measuring-distance range in multi-AF, such as full-screen AF.
Today, it is becoming quite common for image pickup devices, such as cameras, to implement multi-AF. Cameras equipped with a distance-measuring apparatus for measuring subject distances at three, five, or seven points on the shooting screen are commercially available in low-price models.
The multi-AF is one-dimensional multi-AF where distance-measuring areas are arranged on a straight line. Recently, there have been signs of the commercialization of two-dimensional multi-AF or area AF.
For example, a camera equipped with a distance-measuring apparatus having an area AF function using as many as 45 distance-measuring areas 17 on the finder view 16 has been commercialized and put on the market.
In such conventional multi-AF, complex calculations, such as distance-measuring calculations, must be repeated as many times as the number of distance-measuring areas increases. To improve the time-lag, various inventions have been disclosed.
For example, Jpn. Pat. Appln. KOKAI Publication No. 2-158705 has disclosed the technique for acquiring pieces of subject distance information in a first distance-measuring mode in which the distances to points on the subject are measured roughly, selecting the subject presenting the subject distance corresponding to the shortest distance from the acquired pieces of information, and measuring the distance only to the selected subject with high accuracy in a second distance-measuring mode, thereby improving the time-lag.
Furthermore, Jpn. Pat. Appln. KOKAI Publication No. 63-131019 has disclosed a technique which is based on the assumption that, in active AF, the closest main subject is present at the place where the amount of light reflected from the projected light is the greatest and which omits distance-measuring calculations for parts where the amount of reflected light is small, thereby improving the time-lag.
Since all the conventional AF methods have used active AF, they have improved the time-lag remarkably. When they attempt to perform full-screen AF or the like, however, a set of floodlight elements and a set of light-receiving elements cannot avoid becoming very large, which is an obstacle to putting the device to practical use.
In contrast, passive AF would miniaturize the light-receiving elements much more than active AF, causing no obstacle to putting the device to practical use. Thus, passive AF is more suitable for wide-range multi-AF, such as full-screen AF, than active AF.
In this connection, Jpn. Pat. Appln. KOKAI Publication No. 62-103615 has disclosed the technique for performing rough correlation operation on distance-measuring areas, selecting one of the distance-measuring areas on the basis of the result of the operation, and then performing high-accuracy correlation operation on only the selected distance-measuring area, thereby improving the time lag by passive AF.
The rough correlation operation is performed by thinning out sensor data items, such as using every other sensor data item in calculations, but can never be omitted. Thus, although active AF has a higher efficiency of time-lag measures than passive AF, both types of AF produce the same effect.
A recently proposed solution to the problem of which of passive AF and active AF is more suitable for wide-range multi-AF, such as full-screen AF, is a distance-measuring method using hybrid AF. In hybrid AF, which is now in use, a steady-state light removing circuit for removing steady-state light is provided for each light-receiving element in a passive sensor. A passive operation is performed, when the steady-state light removing function is disabled, whereas an active operation is performed when the steady-state light removing function is enabled. Jpn. Pat. Appln. KOKAI Publication No. 10-336921 has disclosed such a steady-state light removing circuit. Products using hybrid AF are already available on the market.
To perform wide-range multi-AF, such as full-screen AF, time-lag measures are essential. Up to now, however, a measuring-distance apparatus provided with an effective distance-measuring system and time-lag measures has not been available. Presently, therefore, time-lag measures are taken using high-speed, expensive CPUs or microcomputers at the sacrifice of cost. Therefore, the prior art distance-measuring apparatus has the disadvantage of having a large time lag because of insufficient time-lag measures.
It is, accordingly, an object of the present invention to realize, without a rise in cost, and provide a high-accuracy distance-measuring apparatus which has a smaller time lag, enables faster operation, and assure a high reliability of the result of distance measurement.
According to a first aspect of the present invention, to accomplish the foregoing object, there is provided a distance-measuring apparatus comprising: a pair of integration-type light-receiving sensors which receive light from a subject and produce a subject image signal; a light-projecting section for projecting light onto a subject; a steady-light removing section for producing an image signal by removing the steady-light component from the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting light onto the subject; a first distance-measuring section for measuring a subject distance on the basis of the image signal the steady-light removing section has produced by removing the steady-light component from the subject image signal; a sensing area setting section for causing the first distance-measuring section to operate for a specific time and setting a sensing area corresponding to a specific integration value range including the maximum component value of the integration signal of the reflected signal component obtained from the operation of the first distance-measuring section; and a second distance-measuring section for measuring the subject distance on the basis of the result of the integration-type light-receiving sensors integrating the sensing area set by the sensing area setting section on the basis of the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting no light onto the subject.
According to a second aspect of the present invention, there is provided a distance-measuring apparatus comprising: a pair of integration-type light-receiving sensors which are composed of at least a first sensor and a second sensor, receive light from a subject, and produce a subject image signal; a light-projecting section for projecting light onto a subject; a steady-light removing section for producing an image signal by removing the steady-light component from the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting light onto the subject; a first distance-measuring section for measuring a subject distance on the basis of the image signal the steady-light removing section has produced by removing the steady-light component from the subject image signal; a sensing area setting section for causing the first distance-measuring section to operate for a specific time and setting not only a first sensor sensing area corresponding to a specific integration value range including the maximum component value of the integration signal of the reflected signal component obtained from the operation of the first distance-measuring section but also a second sensor sensing area to the area obtained by shifting the area corresponding to the first sensor sensing area by a specific amount; and a second distance-measuring section for measuring the subject distance on the basis of the result of integrating the first sensor sensing area and second sensor sensing area set by the sensing area setting section on the basis of the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting no light onto the subject.
According to a third aspect of the present invention, there is provided a distance-measuring apparatus comprising: a pair of integration-type light-receiving sensors which are composed of at least a first sensor and a second sensor, receive light from a subject, and produce a subject image signal; a light-projecting section for projecting light onto a subject; a steady-light removing section for producing an image signal by removing the steady-light component from the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting light onto the subject; a first distance-measuring section for measuring a subject distance on the basis of the image signal the steady-light removing section has produced by removing the steady-light component from the subject image signal; a sensing area setting section for causing the first distance-measuring section to operate for a specific time and setting not only a first sensor sensing area corresponding to a specific integration value range including the maximum component value of the integration signal of the reflected signal component obtained from the operation of the first distance-measuring section but also the second sensor sensing start address to the address obtained by shifting the address corresponding to the first sensor sensing start address by a specific amount and further a second sensor sensing area in the range of a specific amount from the second sensor sensing start address; and a second distance-measuring section for measuring the subject distance on the basis of the result of integrating the first sensor sensing area and second sensor sensing area set by the sensing area setting section on the basis of the subject image signal from the pair of integration-type light-receiving sensors, with the light-projecting section projecting no light onto the subject.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.